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Skema Jawapan Peperiksaan Pertengahan Tahun 2012 Kertas 2 Tingkatan 5

QUESTION NO Marking Criteria MARKSUB TOTAL

1(a)

(i) Nucleon number of an element is the total number of protons and neutrons in its atom

1 9

(ii) 35 – 17 = 18 1

(iii) shows nucleus and three shells occupied with electron Label 12 proton, 12 neutron

1 +1

(iv) Number of electrons = 20 1

(b) (i) Uniform scale for X-axis and Y-axis and labelled Tranfer of point Smooth cuve and correct form of the graph

111

(ii) Dotted line on the graph from the horizontal line to Y-axis at 80oC.

1

2(a)

(i) 0.25 mol0.25x 6.02 x 1023 // 1.505 x 1023molecules

11

10

(ii) number of mole of CO2 = 6.0 24.0 // 0.25 mole

0.25 x 44 // 11g

1

(b) (i) Chemical formula that shows simplest mole ratio of each atom of each element in the compound

1

(ii) Mg = 2.4g , O = 1.6g 1+1(iii) 1 : 1 1(iv) MgO 1

(v) To allow oxygen enter the crucible 1(vi) Copper is less/almost not reactive metal 1

3(a)

Chemical cell 1 10

(b) Cu2+, H+, SO42- , OH- 1

(c) (i)(ii)(iii)(iv)

label (-) at zincFrom zinc to copper through the external circuitCopper electrode become thickerCu2+ + 2e à Cu

1111

(d) (i)(ii)

(iii)

Copper anode become thinnerCopper atom release electron//copper atom ionize to form Copper ion and dissolve in solution.Copper metal

1111

1


No5

Explanation Mark ∑ Mark

(a)(i) Able to mark the strongest alkaline solutionAnswer

SolutionLarutan

P Q R S

√

1 1

(ii) Able to explain why S is the strongest alkaline solutionSample answer

1. S ionized / dissociate completely / fully in water2. Produced higher/highest concentration of hydroxide ion

11 2

(b)(i) Able to name neutralisation processAnswerNeutralisation 1 1

(ii) Able to name a suitable indicator for the reactionSample answerPhenolphthalein // methyl orange // universal indicator 1 1

(iii) Able to state the colour changes based on the named indicator Sample answerPink to colourless // YELLOW to orange // purple to green 1 1

(iv) Able to write the ionic equation for neutralization processAnswerH+ + OH- → H2O 1 1

(c)(i) Able to calculate to water needed for dilutionAnswerM1V1 = M2V20.1(5.0) = M (20) M = 0.025 mol dm-3

11 2

2

4 (a) Alkene 1 10(b) CH3 –CH─ CH3 // H-CH-CH2-CH3

│ │ OH OH

1

(c) (i) 2C3H6 + 9O2 → 6 CO2 + 6H2O 1(ii) Gas is bubbled through lime water.

Lime water turns cloudy1+1

(d) correct set up apparatusLabel

1

(e) Acidified potassium dichromate(VI) solution 1

(f) (i) C2H5COOC3H7 Label C2H5COOC3H7 1+1

(ii) Float on the water. 1


(ii) Able to state the number of ion in the solution after dilutionSame

1 1

Total 10

No6

Explanation Mark ∑Mark

( a ) Able to draw a complete, functional and label the apparatus set-up

1. Functional of apparatus: Clamp the burette, dotted line for water and hydrochloric acid, end of delivery tube below water level in the basin.2. Label: Hydrochloric acid/ HCl, calcium carbonate/ CaCO3, water

1

1 2

(b) Able to draw the graph with these criterion:

1 Labelled axis with correct unit 2 Uniform scale for X and Y axis & size of the graph is at least half of the graph paper 3 All points are marked4 Correct shape, Curve is smooth and start from origin point

1

111 4

(c)(i) Able to draw the tangent and show the working and correct unit 1 Correct tangent at 90 second on the graph 2 Show calculation of the tangent with correct answer and unit Range ( 0.10 – 0.17 ) cm3s-1

1

1 2

(ii) Lower // accept one value than answer in c (i) 1 1

(iii) The concentration of the acid decreases 1 1

Total 10

3



7 (a) (i) 2.5 1

5

(ii) - Atom W is in Group 15 and Period 2 - Because it has 5 valence electrons and 2 shells occupied with electrons.

1+11+1

(b) (i) - reacts explosively// rubidium melts// produced ‘hissing’ sound// produced fire// move rapidly. [any two]

1+1

5

(ii) 2Rb + 2H2O à 2RbOH + H2 - reactant and product- balance equation

11

(iii) Do not holding the metals with bare hand// wear safety goggles/gloves // kept metals in paraffin oil // no flammable substance near the burning metals.

1

(c) (i) ionic compound: Magnesium oxide, sodium chlorideCovalent compound: ethanol, hexane

11

(ii)

1+1

1+1

1+1

4

property Ionic compound Covalent compoundMelting point/ boiling point

Explanation:

MgO/NaCl is high

The forces between Mg2+/Na+ ion and O2-

/Cl- ions are strong.

More heat energy needs to overcome the forces.

C2H5OH/C6H14 is low

The forces between C2H5OH/C6H14 molecules are weak.

Less heat energy needs to overcome the forces.

Electrical conductivity

Explanation:

Conduct in molten state or aqueous.

The freely moving ions are able to carry electrical charges.

Not conduct electricity.

Neutral molecules are not able to carry electrical charges.

Solubility

Explanation:

NaCl is soluble in water.r: MgO

Water molecule is polar solvent.

C2H5OH/C6H14 is soluble in benzene/ toluene / any organic solvents.The attraction forces between molecules in solute and solvent are the same.


1+1

1+1

Max 10


8 (a) - Industries emit (acidic gases)/(sulphur dioxide).- These gases dissolve in rainwater forming acid rain.- The rain water has a higher concentration of acid.- more collisions between (reacting particles)/(metal and acid) to occur.

1111 4

(b) (i) Zn + 2HCl à ZnCl2 + H2HCl : H2 = 2 : 1Mole of H2 = ½ x 0.4 x 50/1000// 0.01Volume of H2 = 0.01 x 24 // 0.24 #dm3#

1111 4

4

3

(ii)

- Axes are labels with units- Curves I, II and curve III are leveling started

at 10 and 5 minutes respectively.- The gradient of curves II and III are more

steep than curve I- Volume of graph level off in Exp. II is 0.24

dm3 and 0.12 dm3 in Exp. I and III.

11

1

1

(iii) I: rate = 0.12 x 1000/10 x 60 // 0.2 1

5


II: rate = 0.24 x 1000/10 x 60 //0.4III: rate = 0.12 x 1000/5 x 60 // 0.4

11

(iv) Experiment I and Experiment II:- The initial rate of reaction in experiment II is higher.- The concentration of hydrochloric acid in experiment II is higher.- The frequency of collision between zinc atoms and hydrogen ions is higher.- The frequency of effective collision also increases.

Experiment I and Experiment III:- The initial rate of reaction in experiment III is higher.- The powdered zinc has a larger total surface area.- The frequency of collision between zinc atoms and hydrogen ions is higher.- The frequency of effective collision also increases.

1

1

1

1

1

11

1 8

No9

Explanation Sub-marks

∑ marks

(a)(i) Able to state the meaning of fat Sample answer:Esters of glycerol and fatty acids 1 1

(ii) Able to compare between the saturated and unsaturated fat correctly Sample answer:

1

1

1

1 4

6

Saturated fat Unsaturated fat

Has carbon-carbon single bond

Sources from animals

Has high melting point

Solid at room temperature

Has carbon-carbon double bond

Sources from plants

Has low melting point

Liquid at room temperature


(iii) Able to state two importances of fats to our body

Sample answer:

1. Fats surround and protect vital organs.2. Fats molecules form the protective membrane of cells.3. Fats store energy as body fat.4. Fats release energy during cell respiration.5. Fats under the skin is to keep our body warm6. Fats help to carry fat-soluble vitamins which are essential for good

health.

[Any 2]

2

(iv) Able to describe the effect of fats to our health

Sample answer:1. Raise the cholesterol level2. Fats deposited on arteries/veins3. Cause heart attack // Cause high blood pressure

OR1. Fats deposited in body tissues2. Obesity

3 Cause heart attack // Cause high blood pressure

111

OR111 3

(b)(i) Able to state the meaning hydrogenation

Sample answer:

Hydrogen / H2 reacts with unsaturated fats to produce saturated fats. // Hydrogen / H2 reacts with unsaturated fats to convert C = C to C - C

1 1

(ii) Able to describe the process

Sample answer:1. Hydrogen pass over oil/fat 2. presence of nickel/platinum and hot / 1800C / high temperature oil3. Carbon-carbon double bond in palm oil becomes carbon-carbon

single bond // H H

– C = C – + H2 – C – C –

H H H H

4. Solid formed// margarine formed

11

1

14

7


(c) Able to explain why the latex coagulatesSample answer:

1. Bacteria/microorganism produce lactic acid/hydrogen ions in latex. r: [acid is added into latex]

2. Lactic acid/hydrogen ions neutralise the negative charged membrane.

3. Rubber particles collide with each other.4. Membrane breaks5. Rubber molecule combine with one another

1

1111 5

Total 20No10

Explanation Mark ∑ mark

(a) Able describe how sulphuric acid is produced

1 Sulphur is burnt in the air to form sulphur dioxide2 S + O2 à SO23 Sulphur dioxide is burnt in the air to form sulphur trioxide4 2SO2 + O2 à 2SO35 Temperature : 450 – 550 °C Pressure: 1 atm6 Catalyst used: vanadium(V) oxide, V2O57 Sulphur trioxide is dissolved in concentrated sulphuric acid to form oleum.8 2SO3 + H2SO4 à H2S2O79 Oleum is diluted with distilled water to form sulphuric acid10 H2S2O7 + H2O à 2 H2SO4

11

111

1

1111 10

(b)(i) Able to draw the functional diagram of apparatus set-up and label

1 Functional diagram2 Label [weight, steel ball, block, meter ruler]

Able to name a suitable metal & its alloy

3 Name of metal (can refer to diagram)

11

1

8


(b)(ii)

Sample answer: copper4 Name the alloy(can refer to diagram) Sample answer: brass

Able to describe the experiment.

5 Tape a steel ball bearing to the brass [block]6 Hang a weight of 1 kg above the ball bearing. (can refer to diagram)7 Drop the weight and allow it to hit the steel bearing8 Record the diameter of the dent made on the brass block9 Repeat the experiment using copper block to replace the brass block.10 Observation:

Type of Block Diameter of dent (cm)

Copper

Brass

1 Presence of foreign atoms (in brass) disrupt the orderly arrangement of atoms2 More difficult to slide.

1

11111

1

1

1

Max = 8

2

Total 20

9

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